Nand switch

ABSTRACT

In a memory system, a switch is connected between a controller and multiple non-volatile storage units, where the switch comprises first and second pins, a data bus, and a plurality of enable outputs. Each of the enable outputs of the switch is connected to an enable input of one of the non-volatile storage units. The switch is configured to transmit a signal to enable a communication path between the controller and one of the non-volatile storage units and to receive data over the data bus to be stored in one of the non-volatile storage units when the first and second pins are not asserted. In addition, the switch is configured to receive a command to be executed by one of the non-volatile storage units when the first pin is not asserted and the second pin is asserted. The switch is also configured to receive an address of a storage location within one of the non-volatile storage units when the first pin is asserted and the second pin is not asserted.

BACKGROUND

The storage capacity of solid state drives (SSDs) continues to increase. That is, SSDs are able to support an ever-increasing number of storage units, such as NAND flash memory units. As storage capacity of SSDs increases, it has become increasingly difficult to scale SSD controllers, which are typically implemented on integrated circuit chips, and which are used to write data to NAND flash memory units and to read data from NAND flash memory units through general-purpose input/output (or GPIO) pins and chip enable (or CE) pins.

With an increasing number of NAND flash memory units supported by present-day disks (greater than 2 terabytes of storage capacity), a greater number of connections from SSD controllers to the NAND flash memory units is required. However, allocating more GPIO and CE pins has a disadvantage because allocating more pins would increase the size of the die package required for the manufacture of the SSD controller. Thus, the cost of manufacturing the SSD controller would increase dramatically. Further, laying out an SSD integrated circuit comprising additional NAND flash memory pin connections would also be costly and disruptive to current SSD controller manufacturing processes. Hence, it would be advantageous to provide a mechanism whereby existing SSD controllers can support disks that have NAND flash memory capacity in excess of 2 terabytes.

SUMMARY OF THE DISCLOSURE

According to one embodiment, a memory system is provided. The memory system comprises a controller configured with one or more enable outputs, a plurality of non-volatile storage units, each configured with an enable input, and a switch configured with an enable input that is connected to one of the enable outputs of the controller. The switch is further configured with first and second pins, a data bus, and a plurality of enable outputs, each of which is connected to an enable input of one of the non-volatile storage units. The switch is configured to transmit a signal to enable a communication path between the controller and one of the non-volatile storage units and to receive data over the data bus to be stored in one of the non-volatile storage units when the first and second pins are not asserted. The switch is further configured to receive a command to be executed by one of the non-volatile storage units when the first pin is not asserted and the second pin is asserted and to receive an address of a storage location within one of the non-volatile storage units when the first pin is asserted and the second pin is not asserted.

According to another embodiment, a method of performing read and write operations in a memory system is provided, where the memory system includes a controller connected to multiple non-volatile storage units by way of a switch. The switch comprises first and second pins, a data bus, and a plurality of enable outputs, each of which is connected to an enable input of one of the non-volatile storage units. The method comprises the steps of transmitting a signal to enable a communication path between the controller and one of the non-volatile storage units and receiving data over the data bus to be stored in one of the non-volatile storage units when the first and second pins are not asserted. The method further comprises the step of receiving a command to be executed by one of the non-volatile storage units when the first pin is not asserted and the second pin is asserted. The method also includes the step of receiving an address of a storage location within one of the non-volatile storage units when the first pin is asserted and the second pin is not asserted.

According to another embodiment, a memory system is provided. The memory system comprises a controller configured with one or more chip enable outputs and a switch configured with a chip enable input that is connected to one of the chip enable outputs of the controller and having multiple chip enable outputs. The memory system further comprises multiple non-volatile storage units each configured with a chip enable input that is connected to one of the chip enable outputs of the switch.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram that depicts a memory system according to one or more embodiments.

FIG. 2 is a block diagram that depicts a connection between an SSD controller and a plurality of NAND switches, according to one or more embodiments.

FIG. 3 is a block diagram that depicts a connection between a NAND switch and a plurality of NAND storage devices, according to one or more embodiments.

FIG. 4 is a flow diagram that depicts a general method of enabling and transmitting data over a communication path from an SSD controller to a target NAND storage device via a NAND switch, according to embodiments.

FIG. 5A is a flow diagram that illustrates a method of enabling and transmitting data over a communication path between an SSD controller and a target NAND storage device using a NAND switch, according to a first embodiment.

FIG. 5B is a signal diagram that depicts the timing of signals received by a NAND switch connected between an SSD controller and a target NAND storage device, according to the first embodiment.

FIG. 6A is a flow diagram that illustrates a method of enabling and transmitting data over a communication path between an SSD controller and a target NAND storage device using a NAND switch, according to a second embodiment.

FIG. 6B is a signal diagram that depicts the timing of signals received by a NAND switch connected between an SSD controller and a target NAND storage device, according to the second embodiment.

FIG. 7A is a flow diagram that illustrates a method of enabling and transmitting data over a communication path between an SSD controller and a target NAND storage device using a NAND switch, according to a third embodiment.

FIG. 7B is a signal diagram that depicts the timing of signals received by a NAND switch connected between an SSD controller and a target NAND storage device, according to the third embodiment.

DETAILED DESCRIPTION

FIG. 1 is a block diagram that depicts a memory system according to one or more embodiments. The system depicted in FIG. 1 comprises a solid state disk (SSD) controller 100, a plurality of NAND switches 110, and plurality of NAND storage devices 120. In embodiments, SSD controller 100 is an electronic device that provides a host computer that is connected to it access to NAND memory components. Typically, SSD controller 100 is a semiconductor processor that executes firmware-level code, and which performs various functions that include reading and writing data from and to NAND memory components, caching, error correction, data encryption, and garbage collection. SSD controller 100 communicates with other devices by way of electrical signals, which are typically received and transmitted through “pin” connections. Each pin is capable of transmitting or receiving an electrical signal which represents a binary 0 or 1 value (or bit value). Typically, a 0 value is represented by a low voltage signal, while a 1 value is represented by a high voltage signal. Pins may be categorized, in embodiments, as general purpose input/output (or GPIO) pins, which typically transmit and receive data to be read from or stored to memory. In addition, GPIO pins of SSD controller 100 transmit and receive address data, which, for example, may refer to storage locations within a NAND storage device 120, or, in other cases, may refer to a register of a NAND storage device 120. SSD controllers may also include “chip enable” (or CE) pins. CE pins are typically used to activate one or more devices to which the SSD controller is connected. For example, SSD controller 100 may be connected to an array of NAND storage devices 120. In order to activate one of the NAND storage devices 120, SSD controller 100 may transmit a particular value (either a 0 or 1) over a CE pin that is coupled to the target NAND storage device 120. In some embodiments, transmitting a 0 value serves to activate the target NAND storage device 120. In other embodiments, transmitting a 1 value activates the target NAND storage device 120. Once the target NAND device 120 is activated (or “enabled”), SSD controller 100 may then transmit data to and read data from the target NAND storage device 120. Equivalently, the activation of the NAND storage device 120 enables a communication path between SSD controller 100 and the activated NAND storage device. The transmission of a value over a CE pin in order to activate a device to which SSD controller is connected is referred to herein as “asserting” the CE pin.

As shown in FIG. 1, SSD controller 100 is connected to one or more NAND switches 110. Each NAND switch 110 is configured to be activated by SSD controller 100 (in embodiments, activation is achieved through assertion of a CE pin of the NAND switch 110 that is connected to a corresponding CE pin of SSD controller 100). According to one or more embodiments, each NAND switch 110 includes discrete logic devices and circuitry that enables it to establish a communication path between SSD controller 100 and selected NAND storage devices 120. Once a NAND switch 110 is instructed by SSD controller 100 to establish a communication path between SSD controller and one or more NAND storage devices 120, the NAND switch 110 acts as a conduit for input/output data to be stored to/read from NAND storage devices 120, addresses of storage locations within the NAND storage devices 120, and commands to be executed by the NAND storage devices 120. Further, according to embodiments, each NAND switch 110 may be configured to sever a communication path between SSD controller 100 and one or more NAND storage devices 120. In one or more embodiments, this severing of communication paths may be accomplish by “de-asserting” a CE pin that is connected to the NAND storage device 120 that is located on the communication path that is to be severed. In some embodiments, de-assertion of a pin is accomplished by transmitting a signal on the pin that is opposite to the signal that asserts the pin. For example, if a particular pin is asserted by the transmission of a 0 value in embodiments, such a pin is de-asserted by transmitting a 1 value over it.

As is further shown in FIG. 1, each NAND switch 110 is connected to one or more NAND storage devices 120. According to embodiments, a NAND switch 110 receives a command from SSD controller 110 to select one or more NAND storage devices 120 to which the NAND switch 110 is connected. As previously mentioned, selection of a NAND storage device 120 by NAND switch 120 enables a communication path between SSD controller 100 and the selected NAND storage device 120. Further, selection may be performed, in one or more embodiments, by asserting a pin of the NAND switch 110 that is connected to a corresponding pin of the NAND storage device 120. In embodiments, each NAND storage device 120 is a non-volatile semiconductor memory device, where stored data persists even when the device is not electrically powered. NAND storage devices 120 are equipped with CE pins that allow each of the devices to be activated, as well as GPIO pins that serve to transmit and receive commands, addresses, and I/O data.

FIG. 2 is a block diagram that depicts a connection between an SSD controller 100 and a plurality of NAND switches 110, according to one or more embodiments. As shown, SSD controller 100 includes a plurality of output pins, which are denoted in the figures with the prefix “Out.” SSD controller 100 includes an Out_DQ pin, which, in embodiments, may actually comprise 1, 8, or more physical pins. Indeed, the totality of pins that comprise Out_DQ may be referred to as a “data bus.” Data is transmitted over Out_DQ, where the transmitted data may be I/O data to be stored within a NAND storage device 120. Further, data transmitted through Out_DQ may be a command to be executed by a NAND storage device 120, or to be executed by a NAND switch 110. In addition, data transmitted through Out_DQ (i.e., the “data bus”) may be address data, which may refer to storage locations within a NAND storage device 120, or to a register within a NAND storage device 120 or a NAND switch 110. As depicted in FIG. 2, Out_DQ is connected in parallel to each of four NAND switches 110 ₁₋₄. Out_DQ of SSD controller 100 is connected to a corresponding DQ pin (or plurality of pins) of each NAND switch 110, which allows all data transmitted over the data bus to be received by each NAND switch 110, provided the NAND switch 100 is activated.

In FIG. 2, SSD controller 100 also includes Out_CLE and Out_ALE pins. These pins are connected to corresponding CLE and ALE pins of each NAND switch 110. The function of the Out_CLE and Out_ALE pins is to communicate the nature of data to be communicated to a target device (whether a NAND switch 110 or a NAND storage device 120) at some future time. In embodiments, pins are asserted and data is transmitted over a data bus at discrete points in time, referred to as “clock cycles.” In one or more embodiments, SSD controller 100 is equipped with a clock signal generator (not shown in FIG. 2) which allows for the synchronization of pin assertions, data transmissions, command execution by target devices, and the like. Thus, during a given clock cycle, the Out_CLE and Out_ALE pins are asserted according to an assertion pattern. Possible patterns are 00, 01, 10, and 11, where the left bit corresponds to the CLE pin assertion and the right bit corresponds to the ALE pin assertion. This assertion communicates to a target device what sort of data is to be transmitted over the data bus (i.e., through Out_DQ to the DQ pins of the target device) in a subsequent clock cycle.

For example, in one or more embodiments, SSD controller 100 asserts a 0 (or low voltage) on both the Out_CLE pin and Out_DQ pin. This assertion (i.e., “00”) communicates to the target NAND device (in the depiction of FIG. 2, this would be NAND switch 110 ₁) that, during a subsequent clock cycle, I/O data is to be transmitted over the data bus. I/O data is, typically, data that is to be stored within a storage location of a NAND storage device 120.

Continuing with the example, SSD controller 100 may also assert a 1 (or high voltage) on the Out_CLE pin and a 0 on the Out_ALE pin. In the depiction shown in FIG. 2, this communicates to the target device (i.e., NAND switch 110 ₁) that a command is to be transmitted over the data bus during a future clock cycle. Indeed, “CLE” typically stands for Command Latch Enable, and signifies that a command is to be transmitted by a source device and is to be expected (and executed) by a target device.

Further, in embodiments, SSD controller 100 may assert a 0 on the Out_CLE pin and a 1 on the Out_ALE pin. This assertion pattern serves to communicate to a target device that an address is to be transmitted on the data bus during some future clock cycle. Indeed, “ALE” typically stands for Address Latch Enable, which signifies that a target device is to expect the transmission of an address by a source device. Addresses may be storage locations inside of a NAND storage device 120. Addresses may also designate registers inside of a NAND storage device 120 or a NAND switch 110.

According to embodiments, SSD controller 100 may also assert a 1 on both the Out_CLE and Out_ALE pins. As will be described herein, such an assertion pattern is not used by a NAND storage device 120, but is recognized by one or more embodiments of a NAND switch 110. In such embodiments of NAND switch 110, the NAND switch is instructed to recognize a data pattern transmitted over the data bus during a future clock cycle, where such data pattern is used by the NAND switch to activate one or more NAND storage devices 120.

As shown in FIG. 2, SSD controller 100 also includes Out_RE and Out_WE pins. An Out_RE pin is a “read enable” pin. The Out_RE pin is connected to a corresponding RE pin of a target NAND switch 110. In embodiments, the signal transmitted over the Out_RE pin communicates to a target device (typically a NAND storage device 110) to output a current data value located at a given storage location within the target device, and to increment an internal address counter to reference a subsequent storage location. The Out_WE pin is a “write enable” pin. As shown, the Out_WE pin is connected to a corresponding WE pin of a target NAND switch 110. In embodiments, the signal transmitted over the Out_WE pin triggers a target device (i.e., a NAND storage device 120 or NAND switch 110) to read data on the data bus (i.e., through the data pins comprising DQ). This behavior may be referred to as “clocking” data into the target device (e.g., addresses, I/O data, or commands). In embodiments, a target NAND switch 110 (or NAND storage device 120) reads the data transmitted to it over the data bus at the rising edge of the signal transmitted over the Out_WE pin.

In addition, SSD controller 100 includes a plurality of Out_CE pins. As mentioned previously, CE typically stands for “chip enable.” As shown in FIG. 2, SSD controller 100 includes four output CE pins, namely, Out_CE0, Out_CE1, Out_CE2, and Out_CE3. In other embodiments, SSD controller 100 may include more or less output CE pins. As shown, each of the Out_CEn pins of SSD controller 100 is connected to a corresponding CE pin of a NAND switch 110. Thus, Out_CE0 is connected to the CE pin of NAND switch 110 ₁, Out_CE1 is connected to the CE pin of NAND switch 110 ₂, Out_CE2 is connected to the CE pin of NAND switch 110 ₃, and Out_CE 3 is connected to the CE pin of NAND switch 110 ₄. In embodiments, SSD controller 100 asserts one or more of its Out_CEn pins in order to activate the corresponding NAND switch 110 to which the Out_CE pin is connected. For example, SSD controller 100 asserts Out_CE0 in order to activate NAND switch 110 ₁. It should be noted that, until a NAND switch 110 has been activated (or “enabled”) by way of assertion of its CE pin, such NAND switch 110 is not activated and will not recognize any data transmitted to it over the data bus (i.e., its corresponding DQ pins), nor will it recognize the assertion of its CLE, ALE, RE, or WE pins. Further, SSD controller 100 may also “de-assert” any or all of its Out_CEn pins in order to deactivate an already active NAND switch 110. In one or more embodiments, de-assertion of a NAND switch 110 may be performed by asserting a 0 value (or low voltage) on the Out_CEn pin that is connected to the CE pin of the NAND switch 110 that is to be deactivated.

As was previously described, each of the NAND switches 110 depicted in FIG. 2 includes pins DQ, CLE, ALE, RE, WE, and CE, which are coupled to corresponding output pins of SSD controller 100. Further, each of the NAND switches 110 includes output pins that transmit data to other devices that the NAND switches 110 are connected to. According to the embodiment depicted in FIG. 2, each NAND switch 100 includes an Out_DQ pin (or set of pins, as the case may be), which represents a data bus output for the switch. Thus, in some embodiments, data that is received by a NAND switch 110 over the data bus through pins DQ is subsequently transmitted over pins Out_DQ. Further, each NAND switch 110 depicted includes four Out_CE pins, namely, Out_CE0, Out_CE1, Out_CE2, and Out_CE3. These CE pins perform a similar function as the Out_CE pins of SSD controller 100, that is, to activate (or enable) communication with a device to which a particular CE pin is connected. Such a device is typically a NAND storage device 120, although connection from a NAND switch 110 to other types of electronic devices is contemplated and is within the scope of the present invention. Further, although each NAND switch 110 is depicted as having four Out_CE pins, it should be noted that other embodiments include less or more Out_CE pins than the embodiment depicted in FIG. 2. Further, NAND switches 110 may also include other output pins (such as clock signal pins, as well as ALE and CLE pins), and it is noted that such embodiments are also within the scope of the present invention.

FIG. 3 is a block diagram that depicts a connection between a NAND switch 110 and a plurality of NAND storage devices 120, according to one or more embodiments. In the embodiment depicted in FIG. 3, a single NAND switch 110 is connected to four NAND storage devices 120 ₁-120 ₄. As was also shown in FIG. 2, NAND switch 110 includes a CE pin (over which communication to NAND switch 100 is activated), as well as CLE, ALE, RE, and WE pins. The functional behavior of each of these pins is the same as described previously with respect to FIG. 2. In addition, NAND switch 110 includes an Out_DQ pin (or set of pins), which serves as an output data bus for the switch. As shown, Out_DQ (i.e., the output data bus) is connected, in a parallel fashion, to each of the NAND storage devices 120 ₁₋₄. The connection of the data bus to each of the NAND storage devices 120 is made at a corresponding DQ pin for each of the storage devices. The NAND switch 110 also includes an Out_CE pin that is separately connected to each CE pin of the NAND storage devices 120. Thus, as shown, Out_CE0 is connected to the CE pin of NAND storage device 120 ₁, Out_CE1 is connected to the CE pin of NAND storage device 120 ₂, Out_CE2 is connected to the CE pin of NAND storage device 120 ₃, and OutCE3 is connected to the CE pin of NAND storage device 120 ₄.

In embodiments, NAND switch 110 is configured to receive an indication from SSD controller 100 (depicted in FIG. 2) to enable a communication path from SSD controller 100 to one or more target NAND storage devices 120. As previously mentioned, this eliminates the necessity for an SSD controller to allocate a large number of GPIO or CE pins to support connectivity to a large number of NAND storage devices. Embodiments of NAND switch 110 receives an indication to enable a communication path by way of the CLE and ALE pins, and, subsequently, through data received from the data bus through pins DQ. In other embodiments, NAND switch 110 may receive a command to set a feature (or internal component) of the switch to serve as an indicator as to what NAND storage device 120 SSD controller 100 is to communicate with. In these embodiments, NAND switch 110 is a device that interacts with SSD controller 100 and NAND storage devices 120 using some well-known protocol (such as Toggle/ONFI). In still another embodiment, NAND switch 110 may receive a manufacturer-specific command (i.e., a command that is not a part of the Toggle/ONFI command set) which serves as the indicator that NAND switch 110 is to enable a communication path from SSD controller 100 to one of the NAND storage devices 120.

After receiving the indication to enable the communication path (regardless of the method by which such indication is received), NAND switch 110 asserts the appropriate Out_CE pin in order to enable the desired communication path. For example, if SSD controller 100 is to store data to NAND storage device 120 ₁, then a communication path between the controller and the storage device must be enabled. Thus, SSD controller 100 instructs NAND switch 110 to enable that path and, once the path is enabled, NAND switch 110 serves as a transmission link in that path. The path is enabled by NAND switch 110 asserting Out_CE0, which is connected to the CE pin for NAND storage device 120 ₁. This activates a communication path to NAND storage device 120 ₁ and communication is thus enabled from SSD controller 100 to NAND storage device 120 ₁ by way of NAND switch 110. Thus, data that is transmitted from SSD controller 100 to be stored at a storage location within NAND storage device 120 ₁ is transmitted from SSD controller 100 to NAND switch 110 (using the data bus between Out_DQ of SSD controller 100 and DQ of NAND switch 110), and then from NAND switch 110 to NAND storage device 120 ₁ (using the data bus between Out_DQ of NAND switch 110 and DQ of NAND storage device 120 ₁).

FIG. 4 is a flow diagram that depicts a method 400 of enabling and transmitting data over a communication path from an SSD controller 100 to a target NAND storage device 120 via a NAND switch 110, according to embodiments. Method 400 begins at step 410, where an enable signal is received by the NAND switch 110. In embodiments, the enable signal is received via the CE pin of NAND switch 110. At step 420, a NAND selection command is received. The selection command may be received through different means, as will be described herein. In addition, the NAND selection command may be received over one or more clock cycles, depending on how the command is transmitted from SSD controller 100 and on how the command is structured (i.e., whether the complete command is received over the data bus, in a register, or through pins other than the data bus).

Next, at step 430, once the command has been received, NAND switch 110 selects the target NAND storage devices 120 based on the received command. In embodiments, selection of a target NAND storage device 120 is performed by asserting appropriate output CE pins. After completion of step 430, a communication between SSD controller 100 and a target NAND storage device 120 is established.

At step 440, NAND switch 440 receives data for a target NAND storage device 120. In some embodiments, I/O data, a command, or an address is received for the target NAND storage device 120. It should be noted that, at this point of method 400, NAND switch 110 acts as a conduit (or a forwarding device) for SSD controller 100. Thus, at step 450, after receiving the command, I/O data, or address for the target NAND storage device 120, NAND switch 110 sends the command, I/O data, or address on to the target NAND storage device 120. It should be noted that steps 440 and 450 are repeated until the communication path between SSD controller 100 and the target NAND storage device 120 is disabled (or severed). In addition, in embodiments, a two-way communication path between the devices is enabled. This means that NAND switch 110 is capable of receiving data from a source NAND storage device 120 and transmitting such data to SSD controller 100. After step 450, method 400 terminates.

FIG. 5A is a flow diagram that illustrates a method 500 of enabling a communication path between an SSD controller 100 and a target NAND storage device 120 using a NAND switch 110, according to a first embodiment. FIG. 5A is described in conjunction with FIG. 5B, which is a signal diagram that depicts the timing of signals received and transmitted by NAND switch 110 at the various steps in method 500.

Method 500 begins at step 510, where NAND switch 110 receives an enable signal from SSD controller 100. As shown in FIG. 5A, the enable signal is received at an initial time t₀. In embodiments, the enable signal is transmitted by SSD controller 100 by asserting the CE pin of NAND switch 110. After NAND switch 110 receives the enable signal, NAND switch 110 is placed in an active state.

Next, at step 520, NAND switch 110 reads CLE and ALE pins. As shown in FIG. 5A, the CLE and ALE pins are asserted according to an assertion pattern by SSD controller 100 at time t₀. At step 530, NAND switch 110 determines whether the CLE and ALE pins are both asserted to logic “high” (i.e., a logical bit value of 1). If, at step 530, NAND switch 110 determines that both the CLE and ALE pins have been asserted to have a logical value of 1, then method 500 proceeds to step 535.

At step 535, NAND switch 110 receives a write enable signal. As shown in FIG. 5A, the write enable signal, denoted by WE, is received at time t₁. As previously mentioned, in embodiments, the WE signal triggers the NAND switch 110 to read incoming data from the data bus (i.e., from pins DQ).

Next, at step 550, NAND switch 110 reads target NAND selection data from the data bus. The target NAND selection data is transmitted by SSD controller 100 and, in embodiments, is read at a time t₁ on data bus DQ, as depicted in FIG. 5B. As shown in the example depicted in FIG. 5B, the value sent on data bus DQ is a hexadecimal value of 1. In embodiments, NAND switch 110 interprets this value as an indicator of which NAND storage devices 120 should be selected for enablement of a communication path. A hexadecimal value of 1 represents a bit pattern of “0001.” Thus, in one or more embodiments, NAND switch 110 interprets this bit pattern as indicating that a communication path to one out of four of the NAND storage devices 120 connected to NAND switch 110 should be enabled. In this example, the NAND storage device 120 that corresponds to the lowest order bit would be enabled. In the embodiment depicted in FIG. 3, the NAND storage device 120 to be selected is the device that is connected to Out_CE0. Indeed, at step 560, NAND switch 110 selects the target NAND storage devices 120 based on the command received and read from the data bus DQ at step 550. Thus, after step 560, a communication path is enabled between SSD controller 100 and each of the selected NAND storage devices 120.

At step 570 of method 500, NAND switch 110 receives data for the selected target NAND storage devices 120. At step 580, NAND switch 110 sends the data received at step 570 to the selected target NAND storage devices 120. That is, once the communication paths from the SSD controller 100 to the selected target NAND storage devices 120 have been enabled, NAND switch 110 behaves as a conduit (or “pass-through”) device, which relays data from SSD controller 100 to the enabled NAND storage devices 120. In addition, NAND switch 100 also relays data from the enabled NAND storage devices 120 to SSD controller 100. The data that is relayed from SSD controller 100 comprises command, address, and I/O data transmitted over data bus DQ, as well as pin assertions made by SSD controller 100 on pins ALE, CLE, RE, and WE. After step 580, method 500 terminates.

FIG. 6A is a flow diagram that illustrates a method 600 for enabling a communication path between an SSD controller 100 and a target NAND storage device 120 using a NAND switch 110, according to a second embodiment. Method 600 is described in conjunction with FIG. 6B, which depicts a signal diagram that illustrates the timing of signals received and transmitted by NAND switch 110 at the various steps of method 600.

Method 600 begins at step 610, where NAND switch 110 receives an enable signal from SSD controller 100. In embodiments, the enable signal is transmitted by SSD controller 100, which asserts the CE pin of NAND switch 110. As shown in FIG. 6B, the assertion of the CE pin of NAND switch 110 occurs at time t₀.

At step 620, NAND switch 110 determines whether a binary zero value (i.e., a low voltage) is asserted on the ALE pin and whether a binary one value (i.e., a high voltage) is asserted on the CLE pin. As shown in FIG. 6B, the assertion of the ALE and CLE pins of NAND switch 110 occurs, in embodiments, at time t₁. As was previously mentioned, when a zero value is asserted on the ALE pin and a one value is asserted on the CLE pin, embodiments of NAND switch 110 are configured to read a command from the data bus in a future clock cycle. Thus, if NAND switch 110 determines that the ALE and CLE pins are asserted, respectively, with binary values 0 and 1, method 600 proceeds to step 625.

At step 625, where NAND switch 110 receives a write enable signal. As previously mentioned, in embodiments, the write enable signal, denoted by WE in FIG. 6B, is received at time t₁. The WE signal triggers the NAND switch 110 to read incoming data from the data bus (i.e., from pins DQ).

At step 630, NAND switch 110 reads a command from the data bus (i.e., the DQ pins). This step is depicted, in FIG. 6B, as occurring at time t1. At step 632, NAND switch 110 interprets the command read from the data bus and determines if the command is a set features command for a register of the NAND switch 110. In embodiments, a set features command is a command that is part of the Toggle/ONFI protocol. In general, a set feature command that is transmitted to NAND switch 110 is followed by data that indicates the feature to be set, as well as data that is used to alter the target feature. Embodiments of NAND switch 110, in addition to the aforementioned input and output pins, may be configured with a register, referred to as a selection register. The selection register is used, in embodiments, to determine communication paths to NAND storage devices 120 connected to NAND switch 110 that are to be enabled. In such embodiments, NAND switch 110 will determine at step 632, whether the set feature command received at time t₁ is intended for the register that is configured with the switch. Note that in FIG. 6B, the register information is transmitted on data bus DQ at time t₂. In addition, it is noted that, also at time t₂, the ALE and CLE pins are asserted with values 1 and 0, which, as was previously mentioned, indicates that the data received on the data bus indicates an address (or, in the case of NAND switch 110, a register).

If NAND switch 110 determines that a set features command for the selection register has been received, method 600 then proceeds to step 635. At step 635, NAND switch 110 receives select data from the data bus and stores the select data in the selection register. In FIG. 6B, the select data is received on the data bus DQ at time t₃. In addition, pins ALE and CLE are set, respectively, to zero (i.e., a low voltage), which indicates that the data received over the data bus is I/O data. Method 600 then proceeds to step 640.

At step 640, NAND switch 110 enables communication paths to target NAND storage devices 120 based on the data stored in the selection register at step 635. As shown in FIG. 6B, a hexadecimal value of 1 is transmitted and received over the data bus. This is equivalent to a bit pattern of “0001.” In one or more embodiments, each bit in the bit pattern corresponds to a CE pin on a NAND storage device 120 that is connected to NAND switch 110. In the example depicted in FIG. 6B, lower order bit 0 corresponds to pin Out_CE0, which is connected to the CE pin of NAND storage device 120 ₁. Hence, in the example of FIGS. 6A and 6B, at step 640, a communication path to NAND storage device 120 ₁ is enabled. Once step 640 of method 600 is completed, a communication path between SSD controller 100 and a NAND storage device 120 is enabled via NAND switch 110. Method 600 then proceeds to step 650.

At step 650, NAND switch 110 receives data for NAND storage device 120 from SSD controller 100. At step 660, NAND switch 110 sends the data received at step 650 to the selected NAND storage device 120. That is, at steps 650 and 660, NAND switch 110 acts as a conduit between SSD controller 100 and a NAND storage device 120. It should be noted that communication from the selected NAND storage device 120 and SSD controller via NAND switch 110 is also possible and is within the scope of the invention. After step 650, method 600 terminates.

FIG. 7A is a flow diagram that depicts a method 700 of enabling a communication path from an SSD controller 100 to a NAND storage device 120 using a NAND switch 110, according to a third embodiment. Method 700 is described in conjunction with FIG. 7B, which depicts a signal diagram that illustrates the timing of signals that are received and transmitted by NAND switch 110 at the various steps of method 700.

As was the case with methods 500 and 600, method 700 begins, at step 710, where NAND switch 110 receives an enable signal from SSD controller 110. As shown in FIG. 7B, the enable signal from SSD controller 110 is received at time t₀.

At step 720, NAND switch 110 determines whether the ALE and CLE pins are set, respectively, to 0 and 1. As mentioned before, asserting the ALE (or address latch enable) pin to 0 and asserting the CLE (or command latch enable) pin to 1 indicates that the data to be received next from the data bus is a command. It is noted that, in FIG. 7B, the ALE and CLE pins are asserted to 0 and 1 at time t₀ by SSD controller 100.

If, at step 720, NAND switch 110 determines that the ALE and CLE pins are set, respectively, to 0 and 1, then method 700 proceeds to step 725.

At step 725, a write enable signal is received. This signal, depicted as WE in FIG. 7B, is received at time t₁. As previously mentioned, the receipt of a WE signal triggers NAND switch 110 to read incoming data from the data bus.

At step 730, NAND switch 110 reads a command from the data bus. Note that, in FIG. 7B, the command is received from the data bus DQ at time t₁. Note also that, in FIG. 7B, the command is depicted as an arbitrary hexadecimal value ZZh. The command received at step 730 is not a command that is part of a well-known protocol, such as Toggle/ONFI. Note that the command that was received in method 600 is a set feature command, which is command that is native to the Toggle/ONFI protocol. By contrast, in the embodiment illustrated in FIGS. 7A and 7B, the received command is a manufacturer-specific command, which is meaningful only to the particular NAND switch 110 connected between SSD controller 100 and NAND storage devices 120. The command indicates to NAND switch 110 that further data that is to be used to determine communication paths for enablement is forthcoming.

Method 700 then proceeds to step 732, where NAND switch 110 determines if the command received at step 730 is a select command. If a select command was received, then method 700 proceeds to step 735. At step 735, NAND switch 110 receives select data from the data bus. As shown in FIG. 7B, the select data is received on data bus DQ at time t2. In FIG. 7B, the select data received is a hexadecimal value of 1, which, as was mentioned before, is equivalent to a bit pattern of “0001.” As was the case for methods 500 and 600, each of the bits in the bit pattern corresponds to an Out_CE pin of NAND switch 110, each of which is connected to a corresponding CE pin of a NAND storage device 120. In the example depicted in FIG. 7B, the low order bit 0 is set to 1, while the other bits are set to 0. This pattern serves as an indicator to NAND switch 110 that a communication path from SSD controller 100 to NAND storage device 1201 is to be enabled through pin Out_CE0.

Method 700 then proceeds to step 740, where a communication path to the target NAND device 120 is enabled based on the select data received at step 735. As shown, the example of FIGS. 7A and 7B indicates that a communication path to NAND storage device 1201 is to be enabled. Thus, at step 740, NAND switch asserts pin Out_CE0, which is connected to the CE pin of NAND storage device 120, as depicted in FIG. 3. Thus, after step 740, a communication path between SSD controller 100 and NAND storage device 120 is enabled.

At step 750, NAND switch 110 receives data for NAND storage device 120 from SSD controller 100. At step 760, NAND switch 110 sends the data received at step 750 to the selected NAND storage device 120. That is, at steps 750 and 760, NAND switch 110 acts as a conduit between SSD controller 100 and a NAND storage device 120. As was previously mentioned, it should be noted that communication from the selected NAND storage device 120 and SSD controller via NAND switch 110 is also possible and within the scope of the invention. After step 760, method 700 terminates.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

Many variations, modifications, additions, and improvements are possible. Plural instances may be provided for components, operations or structures described herein as a single instance. Boundaries between various components, operations and data stores are somewhat arbitrary, and particular operations are illustrated in the context of specific illustrative configurations. Other allocations of functionality are envisioned and may fall within the scope of the disclosure(s). In general, structures and functionality presented as separate components in exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the appended claim(s). 

I claim:
 1. A memory system, comprising: a controller configured with one or more enable outputs; a plurality of non-volatile storage units, each configured with an enable input; and a switch configured with an enable input that is connected to one of the enable outputs of the controller, first and second pins, a data bus, and a plurality of enable outputs, each of which is connected to an enable input of one of the non-volatile storage units, the switch configured to: transmit a signal to enable a communication path between the controller and one of the non-volatile storage units; receive data over the data bus to be stored in one of the non-volatile storage units when the first and second pins are not asserted; receive a command to be executed by one of the non-volatile storage units when the first pin is not asserted and the second pin is asserted; and receive an address of a storage location within one of the non-volatile storage units when the first pin is asserted and the second pin is not asserted.
 2. The memory system of claim 1, wherein the switch is further configured to receive an enabling command to enable the communication path between the controller and the enabled non-volatile storage units.
 3. The memory system of claim 2, wherein one of the enable outputs of the switch is asserted based on data received over the data bus when the first and second pins are asserted.
 4. The memory system of claim 3, wherein the first and second pins are asserted during a first clock cycle and the data is received over the data bus during a second clock cycle.
 5. The memory system of claim 2, wherein the switch is further configured with a selection register that stores a selection value that determines which of the enable outputs of the switch are asserted, and wherein data transmitted over the data bus is stored in the selection register as the selection value.
 6. The memory system of claim 5, wherein the first pin is not asserted and the second pin is asserted during a first clock cycle, a command to store the selection value is received by the switch during a second clock cycle, and the data transmitted over the data bus is received by the switch and stored in the selection register as the selection value in a third clock cycle.
 7. The memory system of claim 6, wherein one of the enable outputs of the switch is asserted based on the selection value.
 8. The memory system of claim 2, wherein the command received by the switch is an enabling command, and the switch is further configured to receive select data after receiving the enabling command.
 9. The memory system of claim 8, wherein: the first pin is not asserted and the second pin is asserted during a first clock cycle; the enabling command is received by the switch over the data bus during a second clock cycle; the select data is received by the switch over the data bus during a third clock cycle; and one of the enable outputs of the switch is asserted based on the select data.
 10. A method of performing read and write operations in a memory system having a controller connected to multiple non-volatile storage units by way of a switch comprising first and second pins, a data bus, and a plurality of enable outputs, each of which is connected to an enable input of one of the non-volatile storage units, the method comprising: transmitting a signal to enable a communication path between the controller and one of the non-volatile storage units; receiving data over the data bus to be stored in one of the non-volatile storage units when the first and second pins are not asserted; receiving a command to be executed by one of the non-volatile storage units when the first pin is not asserted and the second pin is asserted; and receiving an address of a storage location within one of the non-volatile storage units when the first pin is asserted and the second pin is not asserted.
 11. The method of claim 10, further comprising receiving an enabling command to enable the communication path between the controller and one of the non-volatile storage units.
 12. The method of claim 11, further comprising asserting one of the enable outputs based on data received over the data bus when the first and second pins are asserted.
 13. The method of claim 12, wherein the first and second pins are asserted during a first clock cycle and the data is received over the data bus during a second clock cycle.
 14. The method of claim 11, further comprising storing a selection value that determines which of the enable output pins is asserted in a selection register, wherein data transmitted over the data bus is stored in the selection register as the selection value.
 15. The method of claim 14, wherein the first pin is not asserted and the second pin is asserted during a first clock cycle, and further comprising: receiving a command to store the selection value during a second clock cycle; and receiving data transmitted over the data bus and storing said data in the selection register as the selection value in a third clock cycle.
 16. The method of claim 15, further comprising asserting one of the enable outputs based on the selection value.
 17. The method of claim 11, further comprising receiving select data after receiving the enabling command, wherein the enabling command is a select command.
 18. The method of claim 17, further comprising asserting one of the enable outputs based on the select data, wherein: the first pin is not asserted and the second pin is asserted during a first clock cycle; the enabling command is received over the data bus during a second clock cycle; and the select data is received over the data bus during a third clock cycle.
 19. A memory system, comprising: a controller configured with one or more chip enable outputs; a switch configured with a chip enable input that is connected to one of the chip enable outputs of the controller and having multiple chip enable outputs; and multiple non-volatile storage units each configured with a chip enable input that is connected to one of the chip enable outputs of the switch.
 20. The memory system of claim 19, wherein the switch is configured to receive an enabling command to enable a communication path between the controller and one of the non-volatile storage units. 